The idea of using radioactive materials as direct power sources for applications requiring long-lived power sources has been investigated for many decades. Nuclear power sources for deep space probes have been used on many NASA programs especially those that last for decades and where the probes will not have sufficient sunlight for solar panels to operate. Nuclear Batteries, also called atomic batteries, have been developed that attempt to exploit the heat or thermal energy of the radioactive materials as well as the alpha and beta particle emissions energy through various means. Typically these devices tend to be large in comparison to typical electrochemical batteries and also tend to suffer from the emissions of high energy particles including alpha, beta, gamma and neutrons which create human health risks. Besides space probes, small nuclear power sources have been successfully used in devices such as pace makers and remote monitoring equipment.
One area of much research has to do with the direct conversion of beta emissions, i.e. electrons, emitted from radioisotopes that are targeted on a semiconductor material to develop electron-hole pairs and thus generate an electrical current in the semiconductor. All of these devices suffer from very low efficiencies due to the poor electron capture cross section of the designs as well as the semiconductor material itself. This is the same phenomenon that solar cells continue to suffer from even after decades of work and hundreds of billions of dollars of investment.
Researchers have recently begun investigating nanotechnologies with which to implement nuclear power sources. Some of these include the development of micromechanical devices that vibrate or rotate in response to charge build up within the semiconducting materials.
The underlying reason for pursuing the development of nuclear batteries is the much wider goal of developing long lasting, low cost power sources. Along these lines, there are many other fields of research that are producing some interesting and potentially viable power sources. In particular, fuel cells and new electrochemical battery technologies look particularly promising for small, low cost, high density and long-lived power sources but none come close to the energy density and longevity that nuclear power sources offer.
Prior art describes four basic methods of converting radioisotopes into useable energy sources. Three of these require a double conversion process wherein the radioactive sources are used to first generate heat, light or mechanical energy which is then converted into electrical energy. These multiple conversion processes have extremely low efficiencies which puts them at a distinct disadvantage to compete with the fourth method which is referred to as direct conversion.
Of the direct conversion methods, the two that are the most studied are the semiconductor PN junction conversion and the capacitive charge storage conversion. The semiconductor conversion processes, also known as betavoltaics, employs semiconductor technology that suffers from device degradation and very low efficiencies. The capacitive charge storage devices have problems with large size and very high voltages that can reach hundreds of thousands of volts that create materials challenges that can withstand such high voltages. These problems are magnified as the devices are scaled down.
A common problem for all of the prior art is that the amount of energy that can be extracted from the radioactive material is a very low level and at a consistent output which doesn't provide a practical means to support real world applications that demand varying amounts of power at different times.
Of the most relevant descriptions of a nuclear batter disclosed in prior art, Baskis, U.S. Pat. No. 5,825,839, describes a direct conversion nuclear battery utilizing separate alpha and beta sources isolated by an insulating barrier and two charge collector plates, one to collect the negative beta particles and a another plate collect the alpha particles. The two plates become charged and thereby storing the energy in the form of an electric potential the same as a capacitor stores electrical energy in the form of positive and negative charges on parallel plates. This approach utilizes the balanced alpha/beta charge approach as the present invention, but for completely different purposes. In the Baskis disclosure, a load place across the “battery” allows electrons to flow from the negative charged plate to the positively charged plate that is saturated with alpha particles. The recombination of the electrons and the alpha particles is said to produce helium gas which is vented out of the cell. However, this description does not address the recombination of “free” electrons in the metal plate combining with the alpha particles producing He gas directly. However the net effect is the same, the positive plate will become increasingly positively charged by the alpha particles producing a stored electric potential across the device.
The preferred embodiment of the present invention also suggests the use of balanced alpha and beta charges for greater efficiencies, however, such a requirement is not necessary for it to operate. Additionally the present invention can store the energy of the alpha and or beta particles in chemical energy form as a chemical battery as well as in electric potential energy as in a capacitor, as described in alternative embodiments.